Benthic foraminifera as bioindicators of phosphate enrichment in coastal ecosystems

Nutrient pollution, particularly dissolved inorganic phosphate (DIP), is a critical driver of coastal eutrophication, yet its impacts on benthic foraminiferal communities remain poorly constrained. Here, sediments from Jiaozhou Bay were incubated under a gradient of DIP concentrations (0.31-50.0 μmol L^-1) for 3 and 6 months, and community responses were assessed based on high-throughput sequencing of foraminiferal environmental DNA (eDNA) combined with multivariate analyses. Results showed pronounced compositional shifts along phosphate gradients, with assemblages transitioning from Ammonia-dominated under low-DIP to Psammosphaera-dominated under high-DIP. Although alpha-diversity indices did not differ significantly (p > 0.05), beta-diversity revealed clear separation between phosphate treatments (high vs. low) and incubation durations (3 vs. 6 months). Temporal succession featured initial declines in sensitive taxa (e.g., Rotaliida) followed by recovery or dominance shifts, reflecting adaptive restructuring under sustained phosphate exposure. Random forest analysis further identified Reophax, Textularia, and Psammosphaera as robust bioindicators of phosphate enrichment, with abundances strongly correlated to nutrient gradients. Collectively, these findings demonstrate that phosphate stress reshapes benthic foraminiferal communities by favoring stress-tolerant taxa, providing a mechanistic basis for their application in eutrophication monitoring and nutrient management in coastal ecosystems.